Primary control of the torque output of a motor vehicle engine is performed by an accelerator input to an engine control system. The accelerator input may come from an accelerator position sensor (APS) operated by an accelerator pedal. The control system processes the accelerator input as an engine output torque request that is a function of accelerator pedal position. The more the pedal is depressed, the larger the torque request.
The torque request is processed by the engine control system as an element of overall engine control strategy which includes controlling engine operation in ways that enable the engine to comply with relevant tailpipe emission standards. In other words, while the control strategy seeks to operate the engine in accordance with the torque request, operation is controlled in coordination with a tailpipe emission control strategy.
Smoke and NOx are constituents of engine exhaust gas. “Engine-out” exhaust gas is exhaust gas that comes from the engine cylinders and into an exhaust manifold before entering an engine exhaust system. “Tailpipe-out” exhaust gas is exhaust gas that enters the surrounding atmosphere after having passed through the exhaust system. For any of various reasons, the quantities of various constituents in tailpipe-out exhaust gas may not be the same as in engine-out exhaust gas. For example, an exhaust system may include after-treatment, and engine-out exhaust gas may include some unburned fuel that is combusted in the exhaust system for exhaust after-treatment. NOx is typically controlled by controlling exhaust gas recirculation. Smoke, which comprises mostly particulate matter, is typically controlled by controlling air/fuel ratio.
The dynamic nature of motor vehicle engine operation, i.e. accelerations and decelerations, gives rise to transients that impact an engine control strategy and can change the proportions of constituents in engine-out exhaust gas in ways that affect compliance with tailpipe emission regulations.